Circuit board simulation is no longer an option but an inevitable way for most layout designs today. EDA industry is the key factor to promote the rapid development of the global electronic industry, and its market size is as high as $1 trillion. Most of the sales are monopolized by several big companies (measured by the standards of EDA market), and the tools sold are mainly focused on cutting-edge simulation and integrated circuit chip (ASIC, SOC, etc.) design.
However, most electronic layout design engineers only design printed circuit boards, not integrated circuits. The sales of EDA tools and software used in PCBlayout design only account for a small part of the total EDA sales. The reason for this contrast is that many circuit board design engineers do not accept simulation tools, although IC engineers regard simulation as a basic step in the design process. This paper analyzes the reasons for this difference, and introduces the reasons for the rapid development of EDA tools and the areas that engineers should pay attention to.
Reasons for avoiding circuit board design simulation
There are three main reasons for not popularizing simulation in circuit board layout design: complicated use, lack of simulation model and high cost. First of all, up to now, the use of PCB simulation software is still quite complicated, thus forming the concept of “too complicated simulation” among circuit board design engineers. Secondly, the simulation models of many circuits cannot be found, so it is almost impossible to simulate a complete circuit. For example, if there are 200 components on the PCB, of which 193 components can be simulated, but the remaining 7 key components can’t be simulated, what’s the point of imitation: authenticity? More importantly, the price of simulation software is usually very expensive.
Review of printed circuit board design
In the past, the performance of PCB was evaluated by testing the prototype of PCB (usually close to the finished product) with a series of instruments. With the increase of circuit complexity, multilayer boards and high-density circuit boards appeared, and people began to use automatic wiring tools to deal with the interconnection between increasingly complex components. Since then, the working speed of the circuit has been continuously improved, and its functions have been constantly renovated. The physical size of the connection between components and the electrical characteristics of the circuit board have attracted increasing attention.
The development of semiconductor technology has a great influence on PCB design. The complexity of digital devices is getting higher and higher, and the scale of gate circuits has reached thousands or even millions. Now, one chip can complete the functions of the whole circuit board in the past, so that the same PCB can accommodate more functions. Programmable chips have become indispensable devices in many circuit board designs. By the end of 1990s, PCB was not only a platform for supporting electronic components, but also a high-performance system structure, with smaller volume, faster speed, better performance and lower cost.
Development power of circuit board simulation
Fundamentally speaking, the market is a strong driving force for circuit board-level simulation. In the fiercely competitive electronic industry, it is very important to put products into the market quickly. The traditional PCB design method first designs the schematic diagram, then places the components and wiring, and finally uses a series of prototypes for repeated verification/testing. Design modification means time delay, which is unacceptable under the pressure of rapid product market.
So far, the tools chosen by circuit board design engineers are only limited to circuit diagram design, PCB routing and automatic routing tools. When the simulation model is complete and the design engineer is willing to use simulation tools, the engineer will occasionally use simulation software to design, but it is usually only limited to some circuits.
The design goal of “launching the product at the first time” is not just an advertisement, in fact, it is a vital competitive need. Identifying, preventing and correcting design errors in the early stage of product design can prevent circuit board errors. This operation mode is more important than ever before, and PCB simulation is one of the best methods.
EDA supplier’s reaction
According to the development of PCB design and the needs of PCB design engineers, EDA suppliers have taken important steps to eliminate the obstacles that hinder the application of PCB simulation software, thus making the design tools more convenient to operate, more complete models and lower costs. The measures being taken by EDA suppliers are as follows:
1. The integration of schematic diagram establishment and simulation software. PCB engineers master schematic design software and its application. Technically, the software must be able to automatically generate netlist. Now the software can make PCB design engineers create circuit diagrams and automatically output simulation results. Some people may ask, can it be further simplified? The process of drawing can’t be omitted. Why not use a circuit diagram design tool that can automatically draw the simulation circuit at the same time? Therefore, through the integration of circuit diagram design tools and simulation tools, engineers don’t have to consider the low-level coding process, thus avoiding spending too long time learning SPICE simulation tools.
2. In order to improve the simplicity of operation, adding new functions to PCB simulation programs has always been the goal of most EDA suppliers. The realization method is to display the simulation results on the familiar virtual instrument, organize the components according to the part code files and perform “model-free” operation. At this time, you don’t need to know the placement and connection mode of the components, because the intelligent tools understand your design intention. For example, the functions of Multisim, a simulation tool of Electronics Workbench, include oscilloscope, spectrum analyzer, signal generator and logic analyzer, etc. Its appearance and characteristics are no different from those of real electronic measuring instruments. These functions may change the idea of engineers who have always resisted simulation software.
3. The sources of simulation models have increased. In addition to EDA tools’ own device libraries (excellent simulation software suppliers provide most or all of their device models), the websites of device manufacturers are a huge source of design models, and a large number of emerging network “component information companies” can also provide more simulation models for circuit design. From the online device database, layout design engineers can download millions of component models from many manufacturers and choose them. Combining the tools of EDA company with the models provided by component information company can meet the immediate information needs of electronic design engineers. When you choose a design tool, you should pay attention to evaluate whether the software has these functions, and some software even has the ability to design and share on the Internet.
4. The universality of mixed signal design is enhanced. General simulation technology like SPICE is suitable for analog circuits and some digital circuits, including medium scale integrated circuits (MSI) and large scale integrated circuits (LSI). However, it is impossible to use SPICE to model rather complex digital chips (microprocessors, memories, FPGA, CPLD, etc.) at transistor and gate level. The simulation models of these chips are usually written in hardware description languages such as VHDL or Verilog, which can perfectly describe the functions of complex devices. In fact, many programmable chips are designed with VHDL or Verilog language, and their codes can be used for functional simulation.
At present, all simulation technologies can be integrated to realize collaborative simulation. In a single integrated environment, design engineers can get the overall simulation results. The interfaces and communication of different simulation engines (SPICE, VHDL, Verilog, C code, etc.) are opaque to engineers, who only need to care about the chip models that could not be simulated by traditional simulation software in the past.
Now, the simulation of all devices on the circuit board can be realized by using the collaborative model of analog and digital devices based on SPICE, VHDL, Verilog or C code description. For the first time in history, engineers can simulate all the components on the circuit board at the same time, and the simulation process is the same as the real test process. Collaborative simulation provides an ideal test tool for circuit boards containing FPGA and CPLD.
5. The high cost of real software hinders the use of tools by circuit board design engineers, but at present, the price of PCB and PLD simulation software with excellent performance has been lower than 5,000 dollars. With the change of software tools, the number of PC hardware increases exponentially, but the price is getting lower and lower. The reduction of hardware and software cost has actually eliminated the bottle diameter of PCB simulation.
summary
The development of PCB design software has shortened the design cycle and the time for electronic products to be put on the market. Now, many PCB design engineers no longer resist the use of simulation tools. They think that simulation is as important as the establishment of schematic diagram and wiring. Competitive EDA suppliers are forced to provide software with simpler operation, more functions and lower cost.
The next technological leap in PCB design field is probably the application of co-simulation software, which enables digital devices based on HDL model to be simulated simultaneously with analog components and small-scale digital chips based on SPICE model, all of which are components on the same PCB. The increase of EDA component information on the Internet helps to download component data including simulation models from the Internet in time, which is an important condition for accelerating the development of PCB simulation.